The desire to increase productivity and reduce the number of passes over a field, implements with folding booms such as field sprayers have been designed for increased working widths and increased operating speeds. Booms which fold out to define a working width of up to 120 feet or more are now available. As boom size, weight and operating speed increase, large inertial loads are encountered. Building a large boom with reduced weight, easy and repeatable manufacturability and structural soundness and stiffness has become an increasing problem.
The wide booms must fold to achieve a narrowed transport width. Horizontal folding reduces fold height requirements but results in extreme torsional stresses on the boom structure. For horizontal folding, the boom depth dimension is usually minimized, which results in reducing the boom strength and stiffness in the fore-and-aft direction. Over-top folding relieves the torsional stress but can result in unacceptable fold heights with large booms.
A typical boom construction includes a triangular or L-shaped configuration with the base triangle or the lower leg of the L-shaped configuration at the bottom of the boom. Such structural designs that are wider at the bottom than at the top often interfere with desired spray nozzle positioning. Spray nozzle spacing options are limited or operators have to offset certain nozzles from main plumbing line, and uneven spray patterns often result. In the L-shaped designs, most fore-and-aft loads pass through to the centerframe support assembly through the two main lower beams or tubes which advantageously facilitates mounting of boom fold cylinders and tilt pivot structure at the the bottom with the cylinder located at the top. Attempts at providing alternate configurations have met with difficulties, particularly if in the alternate configuration loading is transferred towards the top of the boom. If the fold cylinder and pivot are moved towards the top of the boom and centerframe support assembly to better align with the boom loading, a large separation between the bottom of the boom and centerframe will occur when the boom section is tilted upwardly, while an overlap occurs when the section is tilted downwardly. This separation and overlap cause significant spray pattern problems. Therefore, providing such alternate boom configurations have met with significant design difficulties caused by the load transfers and tilt and fold requirements.
Large booms with tubular designs are often very difficult to manufacture. Individual tube sections can have wide length and angle of cut tolerances. Where tube-to-tube connections are required, such tolerances increase the difficulty and cost of welding tube ends together, and the structural integrity of such tube end weld connections is less than optimum. In addition, conventional tubular boom construction methods require a complex and expensive boom weldment fixture.